Process for the production of tubes of a molecularly oriented plastic

Abstract

A portion of a plastic tube (16) heated to a temperature at which stretching induces a molecular orientation, is clamped in a sleeve (14), a fluid under pressure is introduced into the portion of tube and the sleeve is moved along the portion of tube to cause its progressive radial expansion until it makes contact with a mould (1).

I claim: 
     
       1. A process for the production of a tube of a molecularly oriented plastic, wherein a section of a tube, heated to the temperature at which stretching induces a molecular orientation of the plastic, is placed in a mold and a portion of the section of the tube is clamped in a sleeve and the sleeve is caused to undergo a relative movement along the section of the tube while a fluid under pressure is introduced into the tube so as to cause radial expansion to an internal wall of the mold of portions of the tube at the outlet of the sleeve progressively along the section and the resulting oriented tube is finally cooled and removed from the mold, characterized in that the portions of the tube undergoing radial expansion slide over an annular surface which is located at the outlet of the sleeve and extends up to the internal wall of the mold, said annular surface providing a counter-balancing support to the fluid under pressure, thereby enabling the molecular orientation of the plastic tube to be controlled. 
     
     
       2. Process according to claim 1, characterized in that a fluid whose temperature is substantially equal to the molecular orientation temperature of the plastic is employed for the radial expansion of the portions of tube. 
     
     
       3. Process according to claim 1, characterized in that the friction of the sleeve on the portion of the section of the tube and its relative movement along the section of the tube are controlled so as to cause longitudinal stretching of the section of the tube. 
     
     
       4. Process according to claim 1, characterized in that a section of tube made of a resin based on vinyl chloride is used and is heated to a temperature of between 90° and 130° C. before its radial expansion.